1. Field of the Invention
This invention relates to heliostats, and methods of fabricating the same, useful in concentrating radiant energy upon a remote absorber, and particularly provides a mirror assembly rotatable in azimuthal and elevational directions to track the apparent motion of the sun.
2. Description of the Prior Art
Increasing energy concerns have focussed substantial attention upon new methods for harnessing solar energy. While a large number of heliostat or reflector assemblies have been proposed, it has proven difficult to combine, in a given unit, properties which provide sufficient efficency and response to external loads as well as an economical fabrication cost.
Typical of proposed central-station power plants are those which rely on large arrays of mirrors for concentration of solar energy upon a remote receiver. For example, in a 100 megawatt-electrical solar power plant the outermost mirrors may be 3500 to 4000 feet from the receiver and there can be about 40,000 mirror assemblies, each of 40 square meters, in the mirror field.
It will be evident that the mirror field can be the most costly item in a solar plant and, therefore, lessening the cost of the mirror assemblies is one of the most meaningful steps toward commercializing solar power.
Currently proposed glass mirror assemblies are fabricated by the assembly of a large supporting frame, the mounting of separate mirrors upon the frame, followed by aiming or focussing of the separate mirrors to a common focal point. Such fabrication procedures lead to large individual mirrors to reduce the number of fabrication and aiming operations. Larger mirrors are typically more costly and heavy since the glass thickness is increased due to its fragile nature.
Additionally, proposed mirrors appear to be supported from the back with edges bare, as a peripheral frame does not lend itself to attaching to the mirror supporting frame. Such arrangements are not optimum since the edge of a mirror is the most vulnerable location for crack initiation. Further, back support of mirrors means the glass-silver bond is mechanically loaded, and the bond typically is not as strong as the glass itself. And, leaving the edges of a mirror bare opens the possibility that moisture will penetrate between the glass and silver, leading to peeling of the silver.
Proposed designs which utilize flat mirror panels also tend to lack torsional rigidity. To achieve torsional rigidity in a lightweight structure requires depth in the structure, which is not compatible with proposed flat mirror panel designs. Proposed solutions add substantial weight and cost to the structures.
It will be apparent that provision of a lightweight, sufficiently rigid mirror assembly which alleviates the discussed concerns will hasten the large scale commercial utilization of solar radiant energy.